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June 1s, 1929. w H, FLOQD 1,717,445

PAVEMENT Filed March 22, 1926 lZ T;

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Patented June 18, 1929.

UNITED STATES PATENT oFFl WALTER H. rLooD, or cmcaeo, ILLINOIS,

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application med 'March Y22, i926.. 'serial adsense. ,i i v This invention relates to pavements and more particularly. to a combination asphalt and concrete pavement and a method of forming the same. l

The ordinary asphalt pavement has seyeral defects, the most serious of which is its tendency to displacement resulting in waves and ruts. In order to overcome this fault, itis necessary that the percentage of stability is secured whencthe stone particles are keyed togetheron themselves, the mortary functioning only to fill interstices or voids.' It is, however. impossible to secure this condition by ordinary methods where al1 theingredients are mixed together. y

The advantages of an asphalt p avement are its'-plasticity, pliabilityynon-rigidity, resilience and ease of repair. The defects of cement concrete type of pavement are its rigidity and tendency to crack and disintegrate from stresses imparted by the subgradeand temperatur-echanges.

' It is therefore an object of this inventlon to provide a pavement that shall combine the advantages of .asphalt and concrete pave-` ments, but overcome theirfaults It is a further object of this invention to. provide a pavement comprising crushed rock ,previously coated with asphalt and then rolled or tamped into a coherent yet porous layer, the spaces between said rock being subsequently filled by a cement grout, whereby the rock is rigidly held in place yet sufficient` .resiliency is provided by the asphalt to allow for expansion and compression stresses.

It is a further important object of this invention to povide a method for forming a pavement of combination asphalt and concrete that. shall possess the desired properties, resiliency and great stability.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanving drawings. y

's invention (in a preferred form) is view of thev same.l

ing on the road bed 6 in' anopen condition. vThe mixture may, if desired, .contain some illustrated in the drzmiingsjandy hereinafter more fully described..l

` f On the drawings: f -f v Flgurel is a sectional view offapavement, embodymg the principles of my'invention, 1n the process of constructionef Figure 2 is an enlarged {detail- 'ctional 'Figure 8 is a sectional view offa pavement 1n completed form. j y v l f' Figure 4 is lan enlarged view ofthe same. As shownl on the drawings:

1 My invention `1n general consists in first laying to the desired deptha layer Vof crushed stone,I yindicated bythe reference numeral 1, to which has preferably been previously ap-i plied a coating 2 of asphalt vor similar bituminous compound over the individual particlesv of stone. -The crushed stone 1 should be relatively coarse andt preferably be previously detail seccio'ml graded from about 1% inches in size down to or 1A; inch, but with suicient of the larger sizes toleave the finished mixture after rollsand or'lfnematerial, but notenough to preventthe pieces of stone from bearing on each other firmly. l The coating of asphalt 2 is only suicient to thoroughly cover the individual stones without filling up the voids 4 between thestones. AAfter spreading' the asphalt stone mixture on the road bed and rolling it in in the customary way, -a grout 3 of v,hydraulic cement and water, with or -without sand,` is spread over the asphalt course and forced into it by means of squeegees; rollers'or other suitable means so that all pi-nearly all of the interstices 4 in the'asphalt mixture are filled. The excess is then removed to form a smooth surface-5 and the cement mixture allowed to harden in the usual way. After hardening,

kthe pavement may be 'o ened to tralic, or if to hold the stone together asin the ordinary 110 l concrete pavement. The. asphalt coating 2 on the stone prevents any adhesion of the grout 3 to thc stone. The grout forms a sort of frame work or skelet-on to firmly hold the stone in position and 'prevent displacement but allows a slight movement of the stone from expansion and contraction stresses due to temperature and other causes. It., therefore, does not result in a rigid pavement but is made up of individual particles cemented together by the asphalt and made dense andr resistent to the entrance of' water by means of the cement grout which forms artificial stone particles, the exact size of the voids in the asphalt mixture. Inthis manner a pavement of great. stability is secured which also possesses resiliency and-plasticity and'is nonr1g1 It is not new to make a cement concrete pavement by rolling the stone on the street and pouring a cement grout into and over the stone. This, however, cements all particles together into a rigid slab producing a pavement very similar to the ordinary concrete pavement. The advantage claimed for this method over the ordinary manner of mixing all the materials together in a concrete mixer to cementjthe mineral aggregate firmly together. If it were not for the tendency to displacement, which is the most common and serious fault of an asphalt pavement, a large amount of asphaltcement in the mixture would be beneficial as it increases the pliability and resiliency of the pavement and its resistance to the action of water. Y

This invention permits a wide range of asphalt content and allows the use of a rich 'mixture (that is, high in asphalt) as 4the cement grout supports the stone in its proper place, thus preventing movement under traffic. In thev asphalt mixture employed in this invention any kind of vmineral aggregate of suitable hardness may. be used, such as gravel, slag, limestone, traprock, granite,and the like. and the mixture mav be produced in the ordinary asphalt plant by heating the ingradients or any of the so-called 'cold processes maybe used. In the cement grout any hydraulic cement may be used and if quick hardening is desired, the high alumina cements may be employed.

The essential elements of the invention are an asphalt coated stone mixture in which the the stone particles.

stone is large enough to possess great stability and the subsequent filling of the voids in the asphalt mixture with artificial stone made by the hydraulic cement grout. As pointed out, it is necessary that the stone particles of asphalt mixture are thoroughly keyed together andnhave a firm bearing on each other. This is arecognized practice in road construction, as in the building of water bound macadam pavements coarse stone is thoroughly rolled until a good keying is secured, after which the voids are filled with fine stone screenings, water being used to secure thorough distribution of the screenings. In the ordinary type of asphaltic concrete pavement, sand or fine aggregate must be mixed with the asphalt and stone in order to make the pavement close sufficiently to prevent water and dirt from entering and also to prevent movement of As this sand is mixed with the stone and asphalt at the asphalt plant, it is impossible to retain thev sand or finer particles entirely in the voids but much of it gets between the sto-neparticles and prevents a firm bearing and keying together of the stone. In this invention the grout finds its way into the open voids and cannot prevent the stones from bearing on each other as they are already in proper position. It is a well known fact that the larger stone particles possess greater `stability inthe pavement than the small size. However, 1n an asphaltic concrete, the size of the stone is limited on account of the large voids which the larger stone has so that the larger the particles of stone used the less amount of stone can be used as it requires more fine material to fill the voids. With this invention, stone of any size may be used, voids being entirely iilled by the cement grout.

It will of course be understood that tar or other bituminous compounds might be used' in lieu of asphalt and by the use of the term asphalt herein I also intend to include tar and similar bituminous compounds.

I am aware that -many changes may be made, and numerous details of construction may be varied through a wide rangllwithout departing from the principles of t s invention, and I therefore do not purpose limiting the` patent granted hereon, otherwise than necessitated by the prior art.

I claim as my invention:

1. A pavement comprisin a course of stones individually coated with bituminous material of sufficient thickness to prevent adherence Aof cement to the stones, and a hy-v draulic cement grouting for filling substantially all the voidsin and the interstices be; tween the stones of said course thus forming a skeleton framework for holding the stones in posit-ion and to prevent their displacement, said coating of bituminous materlal serving to bind the stonesto the grouting as well as avpartition medium to` separate the stones from the cement so as to allow for expansion and compression stresses and to thus minimize cracking of the pavement.

2. The process of laying a pavement which consists in grading a given batch of stones, covering each of saidl stones with a bituminous material of sufiicient thickness to prevent adherence of cement to the stones and to allow for expansion` and compression stresses to which the pavement may be subjected, laying a course of said stones, compacting said course so that the stones are4 keyed to each other to form a firm founda- WALTER H. FLOOD. 

